Influence of the background medium on imaging performance of microsphere-assisted super-resolution microscopy.

We demonstrated the importance of the refractive index of the background medium containing the microsphere in microsphere-assisted super-resolution microscopy. We performed numerical simulation and showed that the photonic nanojet properties of a microlens can be optimized by adjusting the index of the background medium surrounding it. Our simulation results, in qualitative agreement with experimental observations, demonstrated that for the same refractive index contrast between the microsphere and its surrounding medium, a high-index microsphere embedded in a medium provides sharper focusing and better imaging quality compared with its low-index counterpart working in air. Our results are of interest for various applications that require optimization of nanojet properties of microspheres, and will inform on the design of novel microparticle-embedded devices for high-resolution imaging.